Gas pipe leakage exposes high threat to life and property. Fixed point gas sensors and particularly those mounted at the manhole of the gas pipes are very helpful in early leakage detection and sending alarms, so that such leakage can be taken care of at the earliest time to avoid explosion. However, the power supply for such system is always a problem in that: 1) usually there's no power cable or at least power outlet; 2) solar battery may not work because of environmental limitations, for example the manhole is on a busy public road. So usually a regular battery is preferred to power the sensing system.
To report the monitored status and send alarms instantly, communication channels are needed to connect to a central monitoring station or to personals on duty. In most cases the gas vendor does not have communication cables routed together with the gas pipes, so reliable wireless communication is always the preferred solution. The major problem for low power solution such as ZigBee is that the transmission distance is too short, for example the normal distance for ZigBee is only 10˜20 meters in 2.4 GHz band, while the manhole distances are usually 50 meters and above. So a convenient solution is using the paid services such as 3G or others.
Though a 3G device can be battery powered, comparing to the budgeted power consumption in manhole applications, it is still considerably high.